Can I Use Two Heating Systems Together? - Ask The Expert Episode 326

Today's question is "Hey Dan, I would like to pair a GSHP with a gas furnace. Currently have a 3 ton A/C with a 100k BTU furnace. These are sized appropriately. I live in northern Indiana. It will be an open loop system. Would like to use the furnace in tandem with the GSHP when heat is called for. What are your thoughts on this?"

Yes they can work together as a hybrid heating system. There are a lot of different ways you can set it up.

3 comments (view/add)
  • David Nunes
    David Nunes
    Posted on 9/27/2022

    I’ve used a heat pump and gas furnace with a traditional two stage thermostat. The client was able to maintain temperature with his solar but on days with larger needs the second stage would use the gas fired furnace. I did use a lock out so they didn’t not run at the same time.

  • Eric
    Posted on 9/27/2022

    I have just replaced a 4-ton gas (propane) with two zones and several servo dampers witht (2) two, 2/3 ton MrCool units (both set to 2 ton). Propane was $2K a year, now it's $0! Plus, the combined A.C. usage is nearly the same as it was before! It is so much more efficient and quiet. The 2K units are 20 seer, whereas the larger units typicaly have a lower seer. Plus, when that side of the house is empty- which it often is, we adjust that thermostat to lower levels, which saves even more.

  • Bob Pearse
    Bob Pearse
    Posted on 9/27/2022

    I think I am correct in adding:

    1. Do not run both GSHP and Gas Furnace at same time. Only use Gas Furnace as Aux heat. Most thermostats such as Nest will handle such a hybrid setup, and will turn off the GSHP and turn on the Gas Furnace when triggered. It is up to you to decide what the trigger point is to switch between GSHP and the Gas Furnace. For regular Heat Pump, outside temperature is used. Not sure for GSHP.

    2. Make sure you put the Gas Furnace BEFORE the coil in terms of air flow. You never want your Gas Furnace to be after the coil since in cooling mode it can create condensation on the Gas heat exchanger which can cause rust and issues with CO leakage.

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